Nuclear chain fission reactions and the steady increase in the development and use of nuclear reactors has produced an ever increasing demand for improved means for transporting the irradiated reaction fuel elements, sometimes referred to as spent fuel elements, to processing plants where significant amounts of the original fissionable material are recovered.
It is recognized, however, that the spent fuel elements contain many highly radio-active fission product isotopes; and that considerable heat is developed by the decay of these radio-active materials. Hence, in the interest of public safety, shipping containers or casks used for transporting these highly radio-active materials must meet very stringent safety requirements. These will include radiation shielding to protect the public from gamma and neutron emissions, and the heat generated by the decay of the radio-active isotopes. Moreover, the cask must have sufficient structural strength to withstand rupture in the event of a highway accident, railroad derailment or the like, and be capable of gamma and neutron containment even when subjected to high temperatures as in the case of an accidental fire.
Of singular importance with respect to inadvertent dropping or dislodgment of a shipping cask from a rail-car or truck, such as might occur in the case of a derailment or highway accident, is means for protecting the cask against rupture. Of the few shipping casks presently in use, most of these have no impact absorbing means as such or at most provide some form of resilient means on one or both ends of the cask for absorbing end-on impact.